SOIL COMPACTION AFTER YARDING OF SMALL-DIAMETER DOUGLAS-FIR WITH A SMALL TRACTOR IN SOUTHWEST OREGON - INTRODUCTION

This study evaluated the effect on soil bulk density of yarding small- diameter Douglas-fir (Pseudosuga menziesii var. glauca (Beissn.) Franc e) with a small tractor. Levels of compaction were measured before yar ding and after one trip, three trips, and six trips by the tractor. Bu lk densities in the surface (10 cm) and subsurface (20 cm) for three t rips and six trips were higher than pretreatment (p less than or equal to 0.10); however, increases in soil bulk density were less than 7 pe rcent and well below standards for detrimental soil compaction used by the USDA Forest Service Pacific Northwest Region. Results from this s tudy support observations made in other compaction studies that much o f the increase in bulk density from ground-based yarding operations oc curs in the first few trips. Other studies, however, show a much highe r increase in bulk density over undisturbed values.